There are both screw compressors which operate in a dry running operating mode and screw compressors which operate in an oil-flooded operating mode. In the latter screw compressors, oil plays a role both as a lubricant and as a sealant during the compression operation itself. In order, however, to avoid any undesired oil ingress into a refrigeration unit which is supplied with compressed refrigerant by the compressor, an oil separator is as a rule provided on a high pressure side of screw compressors of this type.
According to the prior art, an oil separator, for example of a semi-hermetic compact screw compressor, consists of two spaces or volumes separated by a demistor, also called a droplet separator or an aerosol separator made from metal knitted mesh. Compressed gas/oil mixture passes from a pressure pipe which is fed by a compression apparatus or compression unit in the form of at least one screw rotor into the first space or the first volume, in which an oil pre-separation takes place before it passes through the demistor.
Part of the oil is deposited on a bounding wall of the first volume and flows downward on said wall owing to inertia. It is disadvantageous that part of said oil flow passes into the vicinity of the demistor and is mixed again there with the compressed medium, for example refrigerant gas, since it is entrained accordingly by the gas flow.